[SCSI] Fix sense key MEDIUM ERROR processing and retry

1) If the device reports an uncorrectable MEDIUM ERROR, such
as SK MEDIUM ERROR, ASC UNRECOVERED READ ERR, AMNF DATA
FIELD or RECORD NOT FOUND, then: In scsi_check_sense()
return SUCCESS so as to not retry -- the error is
uncorrectable -- this speeds up total processing time.

Signed-off-by: Luben Tuikov <ltuikov@yahoo.com>

Extracted the MEDIUM ERROR piece and
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>